A display device or a display system with which a viewer can feel a strong or natural stereoscopic effect in a two-dimensional image and is less likely to be fatigued is provided. The display system includes a display portion, a detection portion, and a control portion. The display portion is flexible. The detection portion is configured to detect the conditions of a viewer's eye to obtain detection information and to supply the detection information to the control portion. The control portion is configured to extract information on the viewer's fatigue from the detection information and to change the curvature of the display portion on the basis of the information on the viewer's fatigue. The central angle of the curved surface of the display portion is preferably greater than or equal to 20° and less than 90°.